Introduction:Preterm birth affects 8-12 of live births and is associated with the development of elevated arterial blood pressure and aortic narrowing in later life; this suggests that preterm birth may alter the development of arteries. Our objective was to determine the effects of preterm birth, accompanied by antenatal corticosteroid administration, on the structure of the aorta and pulmonary artery, which experience different alterations in pressure flow at birth.Results:At 11 wk, preterm lambs had significantly thicker aortic walls and a smaller lumen, whereas the morphometry of the pulmonary artery was unaffected. Elastin deposition was markedly increased in the aorta and pulmonary artery and smooth muscle content was reduced in the aorta only. In preterm lambs we found injury in the aorta only; controls were unaffected.Discussion:We conclude that moderate preterm birth after antenatal betamethasone can cause injury and persistent alterations in the structure and composition of the aorta, with lesser effects in the pulmonary artery. Our findings suggest that preterm birth may increase the risk of atherosclerosis and aortic aneurysms in later life.Methods:Using an established ovine model of preterm birth, lambs were born at 0.9 of gestation and underwent necropsy at 11 wk after birth; controls were born at term.